Optical energy transducer

ABSTRACT

An optical energy conversion apparatus  10  includes a first impurity doped semiconductor layer  5,  formed on a substrate, and which is of a semiconductor material admixed with a first impurity, an optically active layer  6,  formed on the first impurity doped semiconductor layer  5,  and which is of a hydrogen-containing amorphous semiconductor material, and a second impurity doped semiconductor layer  7,  admixed with a second impurity and formed on the optically active semiconductor layer  6.  The second impurity doped semiconductor layer is of a polycrystallized semiconductor material lower in hydrogen concentration than the material of the optically active semiconductor layer  6.  The average crystal grain size in the depth-wise direction in an interfacing structure between the optically active semiconductor layer  6  and the second impurity doped semiconductor layer  7  is decreased stepwise in a direction proceeding from the surface of the second impurity doped semiconductor layer towards the substrate  1.  By controlling the hydrogen concentration of the second impurity doped semiconductor layer  7,  the number of dangling bonds in the second impurity doped semiconductor layer  7  is significantly decreased to exhibit superior crystallinity to improve the conversion efficiency of the apparatus  10.

TECHNICAL FIELD

[0001] This invention relates to an optical energy conversion apparatusand a method for the preparation thereof. More particularly, it relatesto an optical energy conversion apparatus and a method for thepreparation thereof according to which the apparatus can be reduced inthickness and improved in the conversion efficiency so that theapparatus can be applied to a solar cell device or a photosensor.

BACKGROUND ART

[0002] As a technique for converting a pre-set energy source to anelectrical energy and for capturing the so-converted electrical energy,thermal power generation and nuclear power generation are beingroutinely used. In the thermal power generation, fossil fuels, such ascoal or petroleum, is combusted to generate an energy which is convertedthrough a mechanical energy into an electrical energy. In nuclear powerstation, a nuclear fuel is used to produce a nuclear fission and thenuclear energy so produced is converted into an electrical energy.

[0003] However, in thermal power generation, such problems as globalwarming due to carbon dioxide generated on combusting the fossil fuelare presented. On the other hand, the nuclear power generation isaccompanied perpetually by a problem such as environmental pollution byradioactivity emitted in the reaction of nuclear fission and adverseeffects on the human health.

[0004] That is, if the electrical energy is to be obtained by exploitingthe above-described power generation technique, there is accompanied theeffect on the environment, with the consequence that sustaineddependence on the fossil fuel and on the nuclear energy poses a seriousproblem.

[0005] Meanwhile, a solar cell, as a photoelectric conversion device forconverting the solar light into an electrical energy, has the solarlight as an energy source, so that it has less adverse effect on theglobal environment, so that it is expected to be used extensively asfuture power generating device.

[0006] First, the efficiency of the solar cell, retained to be promisingas next-generation power generating device, is explained with referenceto FIG. 1. The solar cell is a device for converting the incidentoptical energy into an electrical energy. In the current technicallevel, a major part of the incident optical energy is lost in the courseof the conversion process of the light energy to the electrical energy,and of extracting the electrical energy. Among the losses of the lightenergy incident on the solar cell, there are quantum loss, loss due tocarrier recombination, surface reflection loss, absorption by the dopinglayer and loss due to serial resistance.

[0007] The ratio of the optical energy incident on the solar cell to theutilizable electrical energy corresponding to the incident opticalenergy minus the above losses is termed the effective efficiency of thesolar cell. It is a general task in the preparation of the solar cellhow to raise the effective efficiency of the solar cell.

[0008] Meanwhile, the basic structure of the solar cell is a diodehaving a cathode and an anode in a junction of p-and n-typesemiconductors. If light falls on this semiconductor, anelectron-positive hole pair is generated per photon in a level higherthan the band gap proper to the semiconductor. The electron and thepositive hole are isolated from each other by an electrical field of thepn junction and are drawn to the n-type semiconductor and to the p-typesemiconductor, respectively, so that an electrical voltage(photo-electromotive force) is produced across both electrodes. If thecathode and the anode are connected to each other, an electrical poweris produced.

[0009] Apart from the above-mentioned p-n type solar cell, having the pnjunction, there is also a p-i-n type structure comprised of an i-layerof an intrinsic semiconductor area sandwiched between p-type and n-typesemiconductor layers. The solar cell having the p-i-n type structure iswider in breadth than the p-type semiconductor layer or the n-typesemiconductor layer. By the i-layer operating as a depletion area, thesolar cell having the p-i-n type structure is able to absorb incidentphotons on the solar cell to generate as many electron-positive polepairs as possible, as well as to make the light response faster. Theabove-mentioned i-layer becomes an optically active layer of the p-i-ntype solar cell.

[0010]FIG. 2 shows an energy band diagram in case of short-circuitingthe terminals of the p-i-n type solar cell. The Fermi level Ef in thep-type semiconductor layer is slightly above an upper end of the valenceelectron band, with the positive holes being majority carriers and withthe electrons being the minority carriers. On the other hand, the Fermilevel Ef in the n-type semiconductor layer is slightly below theconduction band, with the electrons being majority carriers and with thepositive holes being the minority carriers. The i-layer, which is ajunction of the p-type semiconductor layer and the n-type semiconductorlayer, forms a potential barrier.

[0011] The material which constitutes the solar cell is generallysilicon. The solar cell formed of silicon is roughly classified into acrystalline solar cell, formed of a single crystal solar cell or apolycrystalline silicon, and an amorphous silicon solar cell.

[0012] The crystalline silicon solar cell, which has so far beenmainstream, is high lower at the current technical level than theamorphous silicon solar cell, suffers from the problem that, sincecrystal growth process is energy- and time-consuming, the solar cell isdifficult to mass-produce, while being high in production cost.

[0013] Conversely, the amorphous silicon solar cell is lower inconversion efficiency in the current technical level than thecrystalline silicon solar cell, however, it is higher in opticalabsorption, such that the thickness of the solar cell required forphotoelectric conversion may be {fraction (1/100)} of that of thecrystalline silicon solar cell, and hence the solar cell can beconstructed by depositing a layer of a thinner thickness. Moreover, thesubstrate material of the amorphous silicon solar cell may be selectedfrom a wide variety of materials, such as glass, stainless steel, orpolyimide-based plastic films, such that the amorphous silicon solarcell has such merits that it is broader in manufacturing tolerance andcan be of an increased area. In addition, since the amorphous siliconsolar cell can be reduced in production cost than the crystallinesilicon solar cell, it is expected to be used in future in a wide rangeof fields of application from domestic use to a large-scale powergeneration plants.

[0014] The solar cell, as the smallest unit of the amorphous siliconsolar cell can be prepared, as a result of development of the CVD(chemical vapor deposition) technique, by sequentially depositingsemiconductor thin films having any desired composition or thickness. Ingeneral, a thin film of a phosphorus-containing n-type amorphoussilicon, which is abbreviated below to a-Si:H, an impurity-free i-typea-Si:H thin film and a boron-containing p-type a-Si—H film aresequentially deposited on a substrate, such as glass substrate, to forma solar cell. This solar cell has a potential gradient from its surfacereceiving the incident light towards its back surface. It should benoted that a-Si:H is a hydrogenated amorphous silicon thin film intowhich hydrogen has been captured in forming the silicon thin film. Byhaving hydrogen captured into the amorphous silicon, the lightabsorption coefficient in the visible light area can be increased toincrease the light absorption coefficient in the visible light range.The conversion efficiency of the solar cell can be improved by employingthis sort of the material as the battery material.

[0015] However, if the above-mentioned a-Si:H only is used in preparingthe solar cell, the light having the wavelength not less than 800 nm canscarcely be used because the band gap of a-Si:H is on the order of 1.75eV.

[0016] Thus, such a solar cell has been proposed in which the potentialgradient is produced by impurities and two or more semiconductormaterials having different band gaps are deposited in superposition toprovide for efficient photoelectric conversion of the light beams ofdifferent wavelengths.

[0017] The solar cell having the above-described structure, termed ahetero junction type cell, has been proposed in view of the fact thatthe cell cannot photo-electrically convert the light lower in energythan the band gap of the semiconductor material forming the solar cell,and that the larger the band gap of the semiconductor material, thehigher is the voltage that can be obtained by photoelectric conversion.With the hetero junction type solar cell, the photoelectric conversionefficiency is improved by providing plural semiconductor layers havingband gaps corresponding to the incident light energy.

[0018] The hetero junction type solar cell aims at realizing effectivelight utilization by employing e.g., amorphous silicon germanium, termedbelow a-SiGe:H. However, this a-SiGe:H has a drawback that, although itexhibits more significant absorption to the light of longer wavelengthand hence it is able to enlarge the shorting current, it exhibits anin-gap level formed in the gap higher than that with a-Si:H to decreasea curve factor to lower the conversion efficiency.

[0019] This problem is addressed by varying the composition of a-SiGe:Hand a-Si:H to thereby vary the band gap continuously.

[0020] With this method, the closer the minimum value portion of theband gap of the i-layer to the p-type semiconductor layer as the lightincident side, the optical deterioration may be lowered to improve thedevice reliability. This is due to the fact that the larger thedistribution of the optical absorption in the vicinity of the p-typesemiconductor layer, the higher becomes the degree of collection of thepositive holes. However, there is raised a problem that, if the smallestvalue portion of the band gap is formed in the vicinity of the p-typesemiconductor layer, the band gap of the i-layer in the vicinity of thep-type semiconductor layer becomes smaller to decrease the voltage valuefurther. In addition, in this method, in which the band gap of thei-layer is decreased to increase optical absorption, the curve factor isincreased with the band gap of the i-layer approximately 1.4 eV or less,thus imposing limitations in improving the conversion efficiency despiteincreased light optical absorption.

[0021] There is also proposed a method of providing an amorphous siliconcarbide (a-SiC:H) layer, having a wide gap on the order of 2.1 eV, in aninterface between the p-type semiconductor layer and the i-layer.However, this method suffers a problem that, since it is not possible toform an a-SiC:H layer of a high film quality, the optical deterioration,which may lead to the worsened hole movement following lightirradiation, tends to be increased.

[0022] Meanwhile, in order to accommodate the solar cell to varioususages, it is necessary to respond to the demand for achieving thelightness in the weight of the product, improved productivity, ease inmachining the curved surfaces and for cost reduction.

[0023] The majority of the low melting materials or plastic materialscan be molded to a desired shape at lower temperatures, so thatmachining costs can be advantageously decreased. Moreover, a plasticsmaterial has a merit that it is lightweight and less liable to cracking.Therefore, it is desirable to use the low melting material or plasticsmaterial as a substrate of the solar cell. If the plastic material,especially a general-purpose plastics, such as polyester film, as asubstrate, it becomes possible to improve the productivity significantlyusing a roll-to-roll type manufacturing system employing an elongatedsubstrate.

[0024] However, since the heat resisting temperature of thegeneral-purpose plastics is generally 200° C. or lower, it is necessaryto use a low-temperature film forming process and to realize filmformation to a high film quality in the low-temperature film formingprocess.

[0025] If such materials as Si, Si_(1-x)Ge_(x), Ge or Si_(1-x)C_(x) aresubjected to a film-forming process at a substrate temperature of 200°C. or lower, the resulting film is usually amorphous. In the amorphousfilm, there exist a large number of elements, which serve as nuclei ofre-combination of minority carriers, such as local energy level in theenergy band gap, with the carrier length being shorter than that in asingle-crystal film or a polycrystalline film.

[0026] Therefore, if an a-Si:H film, an a-Si_(1-x)Ge_(x):H film, ana-Ge:H film or an a-Si_(1-x)C_(x):H film, doped with an impurity, suchas a film which has become a p- or n-type semiconductor layer on beingdoped with boron or phosphorus, is used as the p-type semiconductorlayer and/or as the n-type semiconductor layer in the p-i-n type solarcell, the conversion efficiency is lowered due to the lower dark currentratio, thus proving a hindrance to the preparation of a high qualitysolar cell at lower temperatures. Therefore, if these materials areused, the dark current ratio must needs be 1×10⁻³ S/cm or less andmoreover is required to be not less than 1×10⁻² S/cm.

[0027] Moreover, in the p-i-n type solar cell, light absorption in thep-type semiconductor layer or in the n-type semiconductor layer does notcontribute to improvement in the efficiency (so-called dead zone). Thea-Si_(1-x)Ge_(x):H film, an a-Ge:H film or an a-Si_(1-x)C_(x):H film,doped with an impurity, is insufficient in the doping efficiency, sothat the film tends to be depleted. If the a-Si_(1-x)Ge_(x):H film, ana-Ge:H film or an a-Si_(1-x)C_(x):H film is used, the film thicknessneeds to be thicker to a more or less extent to prevent the depletion.So, with this sort of the solar cell, in which the p-type semiconductorlayer or the n-type semiconductor layer is increased in film thickness,the light absorption in these layers is increased to obstruct theimprovement in the conversion efficiency.

[0028] Thus, in the p-i-n type amorphous silicon based solar cell, sucha technique has been proposed in which only the p-type semiconductorlayer doped with an impurity and the i-layer are crystallized todecrease the value of the light absorption coefficient as an index forease in optical absorption to improve the conversion efficiency.

[0029] For example, in the Japanese Patent Publication H-6-5780, thep-type semiconductor layer and the n-type semiconductor layer of thehydrogenated amorphous silicon are irradiated with an excimer laser,whereas, in the Japanese Laying-Open Publication S-63-133578, the p-typesemiconductor layer and the n-type semiconductor layer of thehydrogenated amorphous silicon are irradiated with the YAG-laser forannealing, thereby crystallizing the p-type semiconductor layer and then-type semiconductor layer.

[0030] However, should the laser of an energy strength sufficient tocrystallize the hydrogenated amorphous silicon be directly radiated onthe film surface, the a-Si:H film is flown off under the pressure ofprecipitous hydrogen extraction from within the film, whilst hydrogenpassivated below the poly-Si layer is also extracted to produce films ofinferior optical properties having a large number of dangling bonds.FIG. 3 shows the state of the hydrogenated amorphous silicon film beforeand after irradiation of the excimer laser (ELA) of the aforementionedintensity.

[0031] It may be seen from FIG. 3 that hydrogen is ejected from withinthe hydrogenated amorphous silicon film as a result of laserirradiation. Should hydrogen be ejected from within the film, the filmis destroyed.

[0032] In particular, in a film prepared at lower temperatures, thereare many cases where a large quantity of hydrogen is contained betweenSi networks. In order to evade ablation resulting from sudden warmingand resulting explosion of hydrogen, the operation of so-called hydrogenextraction by raising the temperature to approximately 400° C. in afurnace is required. FIG. 4 shows the manner in which a film iscrystallized by irradiating excimer laser (ELA) on the film from whichhydrogen is extracted as described above.

[0033] In general, the main defect of the amorphous semiconductormaterial in which constituent atoms lack in regularity resides in thedangling bonds of the constituent atoms which are not bonded. Thedangling bond density, indicating the number per unit volume of thedangling bonds, is a measure of the photovoltaic effect, such that, ifthe dangling bond density is high, the light absorption coefficientbecomes higher. If the number of the dangling bonds of amorphous siliconis increased, the dangling bond density is naturally increased, as aresult of which the light absorption coefficient of the hydrogenatedamorphous silicon film, irradiated with the laser light, is increased.

[0034] Should only the doping layer of the hydrogenated amorphoussilicon be crystallized by annealing on laser irradiation, it is notpossible to form a p-i-n type solar cell having a doping polycrystallinefilm of higher quality having only a smaller number of dangling bonds.

DISCLOSURE OF THE INVENTION

[0035] It is therefore an object of the present invention to provide anoptical energy conversion apparatus of a thin type having a highconversion efficiency, and a method for the preparation thereof.

[0036] In one aspect, the present invention provides an optical energyconversion apparatus including a first impurity doped semiconductorlayer, formed on a substrate, the first impurity doped semiconductorlayer being of a semiconductor material admixed with a first impurity,an optically active layer, formed on the first impurity dopedsemiconductor layer, the optically active semiconductor layer being of ahydrogen-containing amorphous semiconductor material, and a secondimpurity doped semiconductor layer, admixed with a second impurity andformed on the optically active semiconductor layer, the second impuritydoped semiconductor layer being of a polycrystallized semiconductormaterial lower in hydrogen concentration than the material of theoptically active semiconductor layer. The average crystal grain size ofthe second impurity doped semiconductor layer is decreased stepwise in adirection proceeding from the surface of the second impurity dopedsemiconductor layer towards the substrate.

[0037] In this optical energy conversion apparatus, micro-crystals areformed in the second impurity doped semiconductor layer so that theaverage crystal grain size will be decreased from the surface of thesecond impurity doped semiconductor layer towards the substrate.

[0038] In another aspect, the present invention provides a method forthe preparation of an optical energy conversion apparatus forming afirst impurity doped semiconductor layer on a substrate, the firstimpurity doped semiconductor layer being of a hydrogen-containingamorphous semiconductor material, forming an optically active layer onthe first impurity doped semiconductor layer, the optically active layerbeing of a hydrogen-containing amorphous semiconductor material, forminga second impurity doped semiconductor layer on the optically activelayer, the second impurity doped semiconductor layer being of anamorphous semiconductor material which is admixed with a second impurityand which is lower in hydrogen concentration than the optically activelayer, and irradiating laser light on the substrate after forming thesecond impurity doped semiconductor layer for laser annealing.

[0039] In a method for the preparation of an optical energy conversionapparatus, after forming the second impurity doped semiconductor layerwhich is lower in hydrogen concentration than the optically activelayer, irradiating laser light on the second impurity dopedsemiconductor layer formed for laser annealing, and crystallizing thesecond impurity doped semiconductor layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0040]FIG. 1 illustrates the efficiency of a solar cell

[0041]FIG. 2 illustrates a band diagram of a p-i-n type solar cell.

[0042]FIG. 3 illustrates the manner in which a film is destroyed byhydrogen on irradiation of excimer laser.

[0043]FIG. 4 illustrates the manner in which a film is destroyed byhydrogen on irradiation of low temperature excimer laser.

[0044]FIG. 5 is a cross-sectional view for illustrating the structure ofa solar cell embodying the present invention.

[0045]FIG. 6 illustrates a first solar cell model used in simulationcalculations for the conversion efficiency.

[0046]FIG. 7 illustrates a second solar cell model used in simulationcalculations for the conversion efficiency.

[0047]FIG. 8 illustrates a third solar cell model used in simulationcalculations for the conversion efficiency.

[0048]FIG. 9 is a graph showing the results of simulation calculationsdfor the conversion efficiency employing a solar cell model.

[0049]FIG. 10 is a graph showing the results of measurement of the UVreflection of a solar cell embodying the present invention.

[0050]FIG. 11 is a graph showing the results of measurement of the FTIRmeasurement of the solar cell shown in FIG. 10.

[0051]FIG. 12 is a first cross-sectional view of the solar cell shown inFIG. 10, as imaged by a TEM.

[0052]FIG. 13 is a second cross-sectional view of the solar cell shownin FIG. 10, as imaged by a TEM.

[0053]FIG. 14 shows the results of measurement by SIMS of the solar cellshown in FIG. 10.

[0054]FIG. 15 is a cross-sectional view for illustrating a specifiedstructure of the solar cell shown in FIG. 10.

[0055]FIG. 16 is a first cross-sectional view for illustrating aspecified structure of a conventional solar cell.

[0056]FIG. 17 is a second cross-sectional view for illustrating aspecified structure of a conventional solar cell.

BEST MODE FOR CARRYING OUT THE INVENTION

[0057] Referring to the drawings, the best mode of carrying out thepresent invention will be explained in detail.

[0058] A solar cell 10 embodying the present invention is hereinafterexplained. The solar cell 10 is shown in cross-section in FIG. 5.

[0059] The solar cell 10 includes a plastics substrate 1. Among thematerials of the plastics substrate, there are, for example, polyesters,such as polyethylene terephthalate, polyethylene naphthalate, orpolycarbonates, polyesters, such as polypropylene, polyolefins, such aspolypropylene, polyphenylene sulfides, such as polypropylene sulfide,polyamides, aromatic polyamides, polyether ketones, piolyimides, acrylicresins, and PMMA. In particular, general-purpose plastics, such aspolyethylene terephthalate, acetate, polyphenylene sulfides,plycarbonates, polyether sulphone, polystyrene, nylon, polypropylene.polyvinyl chloride, acrylic resins and PMMA, are preferred. Iffilm-shaped pasticssubstrate is used, the plastics material ispreferably bi-axially stretched in view of mechanical stability andstrength.

[0060] On the plastics substrate 1 is formed an electrode layer 2 usinga sputtering device. The electrode layer 2 is a transparent electricallyconductive film or a metal electrode.

[0061] As a transparent electrically conductive film, oxides of hightransparency and low resistance, such as ITO, tin oxide, fluorine-dopedtin oxide, zinc oxide-aluminum oxide, are used. If ITO is used, thedoping quantity of tin oxide is preferably 2 to 20 wt %.

[0062] The metals of the metal electrodes may, for example, be Ag, Cr,Mo, Ta or Al.

[0063] Between the electrode layer 2 and the plastics substrate 1, thereis preferably provided an adhesive layer 3 for improving the adhesion ofthe electrode layer 2 and the plastics substrate 1 to each other. As theadhesive forming the adhesive layer 3, an acrylic adhesive, asilicone-based adhesive or an EVA resin based adhesive is preferred.

[0064] The electrode layer 2 may be of a laminated structure comprisedof transparent electrically conductive films and metal electrodes, suchas a laminated structure comprised of ZnO/Al, ZnO/Ag, ZnO/Cr, ITO/Al,ITO/Ag or ITO/Cr. With the layered structure of the transparentelectrically conductive films and metal electrodes, the electrode layer2 prohibits metal diffusion to achieve a high electrical conductiveity.

[0065] On the back surface of the plastics substrate 1, that is on thesurface of the plastics substrate 1 opposite to its surface carrying theelectrode layer 2, there may be formed a back surface barrier layer, notshown. This back surface barrier layer is able to suppress moistureabsorption of the plastics substrate 1, thus preventing the plasticssubstrate 1 from becoming deformed as when the solar cell 10 is exposedto atmospheric pressure from the vacuum vessel of the sputtering deviceor during the solar cell manufacturing process. This back surfacebarrier layer may be formed of silicon oxide.

[0066] A barrier layer 4 may also be formed between the plasticssubstrate 1 and the electrode layer 2. Similarly to the back surfacebarrier layer, the barrier layer 4 may be formed of silicon oxide. Thebarrier layer 4 in such case operaters as a protective layer.

[0067] On the upper surface of the electrode layer 2, pre-set impuritiesare doped to form Si-based amorphphous films, such as a-Si:H film, ana-Si_(1-x)Ge_(x):H film, an a-Ge:H film or an a-Si_(1-x)C_(x):H film. Asthe film forming device, a sputtering device is used. In film forming,the substrate temperature is set to not higher than 200° C. for whichtheplastics substrate is not likely to be damaged, preferably to not higherthan 150° C.

[0068] The Si-based amorphous film, deposited on the upper surface ofthe electrode layer 2, is polycrystallized, using an excimer laser (ELA)to form microcrystals to form a doping layer 5 of, for example, poly-Si,poly-Si_(1-x)Ge_(1-x), poly-Ge or poly-Si_(1-x)C_(x).

[0069] As the excimer laser, ArF excimer laser, XeF excimer laser, XeClexcimer laser or KrF excimer laser, for example, is used. Theirradiation energy and the irradiation time of the excimer laser areselected so that the temperature of the plastics substrate will bemaintained at 200° C. or lower and preferably at 150° C. or lower. Byadjusting the energy of the excimer laser irradiated, it is possible toproduce a film extremely thin in thickness and which is higher in thedoping efficiency.

[0070] It has been ascertained that the crystallization factor of a filmis varied with the energy of the excimer laser irradiated, such that, ifthe film is not completely crystallized but is micro-crystallized, thereare numerous dangling bonds generated in the film, however, when thehydrogenated film is subsequently formed, there occurs passivation sothat the film is turned into a hydrogenated micro-crystallized film(Japanese patent Application H-11-334978, filed on Nov. 25, 1999, byAkio Machida, Gosign D. P., Takashi Noguchi and Setsuo Usui).

[0071] Then, an amorphous layer 6, which may be an a-Si:H film, ana-Si_(1-x)Ge_(x):H film, an a-Ge:H film or an a-Si_(1-x)C_(x):H film, ora layered film thereof, is formed using a PE-CVD device or a sputteringdevice. If the doping film 5 is low in the crystallization factor suchthat the doping film 5 is micro-crystallized, the amorphous layer 6 isformed, at the same time as the doping film 5 is hydrogenated.

[0072] On the upper surface of the amorphous layer 6, an Si-basedamorphous film, such as a-Si:H film, an a-Si_(1-x)Ge_(x):H film, ana-Ge:H film or an a-Si_(1-x)C_(x):H film, having a hydrogenconcentration lower than that of the amorphous layer 6, and which isdoped with a pre-set impurity, or an Si-based amorphous film free ofhydrogen, such as a-Si film, an a-Si_(1-x)Ge_(x) film, an a-Ge film oran a-Si_(1-x)C_(x) film, is formed using a sputtering device.

[0073] The Si-based amorphous film, formed on an upper surface of theamorphous layer 6, is crystallized, using an excimer laser, to form adoping layer 7, such as poly-Si, poly-Si_(1-x)Ge_(x), poly-Ge orpoly-Si_(1-x)C_(x).

[0074] By forming the doping layer 7 in such a manner that the hydrogenconcentration of the doping layer 7 is lower than that of the amorphouslayer 6 or in such a manner that hydrogen content is nil, the dopinglayer 7 can be formed without being damaged by residual hydrogen at thetime of crystallization on irradiation with the excimer laser.

[0075] As shown in FIG. 5, the doping layer 7 is globally crystallized,as a result of irradiation with the excimer laser, so that the dopinglayer 7 becomes a polycrystalline layer in which the average crystalsize of the crystals is decreased stepwise in a direction from thesurface towards the plastics substrate 1.

[0076] The polycrystalline layer, crystallized by the laser light, isformed due to passivation with residual hydrogen slightly extracted fromthe a-Si:H layer of the amorphous layer 6. So, the doping layer 7 hassatisfactory optical properties having only a small number of danglingbonds.

[0077] Meanwhile, it is well-known that the hydrogen concentration inthe amorphous silicon film in general affects the properties of theamorphous silicon film significantly (for example, Paulo V. Santos andWarren B. Jackson; Physical Review B, 46, 1992, p.4595), and that anamorphous silicon film having satisfactory properties may be obtainedfor the hydrogen concentration of 1 to 30% (5×10²⁰ atom/cc to 1.5×10²²atom/cc) or, preferably, of 5 to 25% (2.5×10²¹ atom/cc to 1.25×10²²atom/cc) (see K. Zellama, L. Chahed, P. Sladek, M. L. Theye, J. H. vonBaradeleben and P. Rocai Cabrrocas; Physical Review B, 53, 1996,p.3804).

[0078] If, for a micro-crystal layer, with a crystal size of 1 nm, thevolume take-up ratio of crystals (crystallization ratio) of crystals isapproximately 80%, the density of crystalline silicon is 5×10²² (1/cm³),a micro-crystalline layer with an amorphous domain with the hydrogenconcentration of approximately 5% is supposed to exist therearound, andpre-set calculations are made, it is seen theoretically that if themicrocrystalline interface is completely passivated and hydrogen withthe hydrogen concentration of the order of 5% exists in the amorphousdomain, provided that there exists hydrogen on the order of 6.3×10²¹(1/cm³). Therefore, if the characteristics of the micro-crystallinedomain are taken into account, it is desirable that the amorphous layer6 contains hydrogen on the order at least of 5×10²⁰ atom/cc even afterirradiation with the energy beam of the excimer laser.

[0079] Therefore, the hydrogen concentration of the doping layer 7 needsto be lower than that in the amorphous layer 6 and hence is set to5×10²⁰ atom/cc or less.

[0080] On the upper surface of the doping layer 7 is formed an electrodelayer 8, which is a transparent electrically conductive film. As thetransparent electrically conductive film, oxides of high transparencyand low electrical resistance, such as ITO, tin oxide, fluorine-dopedtin oxide, zinc oxide-aluminum oxide, are used. If ITO is used, thedoping quantity of 2 to 20 wt/% is desirable.

[0081] In this manner, the solar cell 10 comprised of a layeredstructure is fabricated. At this time, the doping layer 7 ispoly-crystallized, with the crystal grain size becoming smaller stepwisefrom the surface of the doping layer 7 towards the plastics substrate 1.As this doping layer 7, other Si-based semiconductor films, such asa-Si_(1-x)O_(x), a-Si_(1-x)N_(x), SiAl, SiGa, SiS or SiSn, may also beused.

[0082] With the solar cell 10, prepared as described above, such acrystalline film having a high doping efficiency can be achieved withoutthermally damaging the plastics substrate 1. The result is that, sincethe doping layers 5 and 7 of the solar cell 10 exhibit high electricalconductivity, the Fermi level can be approached to the valence band orto the conduction band, with the doping layer of the p-typesemiconductor layer or the n-type semiconductor layer, respectively,thus improving the conversion efficiency.

[0083] On the other hand, with the film crystallized with the laser,such a film having a high doping efficiency may be produced incontradistinction from the film obtained with the conventional methodconsisting in checking for the hydrogen quantity at the time of filmformation and forming the film only gradually, so that it is possible tomaintain the gradient of the potential from the light receiving surfaceto the back surface with a p-type semiconductor layer and an n-typesemiconductor layer of thinner thicknesses to improve the crystallinityof SiC which is difficult to crystallize with the prior-art system.

[0084] The fact that the conversion efficiency can be improved bypreparing the solar cell 10 can be confirmed by simulation calculations.

[0085] For example, the simulation calculations of the conversionefficiency can be made using a solar cell model configured as shown inFIGS. 6 to 8.

[0086] The solar cell model, shown in FIG. 6, is such a model having astructure of p⁺a-Si:H/a-Si:H/n⁺a-Si:H, and which is formed in itsentirety by an amorphous silicon film.

[0087] The solar cell model, shown in FIG. 7, is such a model having astructure of p⁺μc-Si:H/a-Si:H/n⁺μc-Si:H, and in which the p- and n-typesemiconductor layers, as doping layers, are micro-crystallized.

[0088] The solar cell model, shown in FIG. 8, is such a model having astructure of p⁺μc-SiC:H/a-Si:H/n⁺=c-Si:H, and in which the p- and n-typesemiconductor layers, as doping layers, are micro-crystallized.

[0089] In making the simulation calculations, it was presumed that thesolar light of AM1.0 was irradiated from the p-type semiconductor layerbased on the method of calculations by Nakamura et al. (Nakamura et al.;Proc. 4th EC PVSEC, Stresa, May 10-14, 1982). The absorption coefficientof the micro-crystallized film was calculated based on the absorptioncoefficient of the crystalline silicon.

[0090]FIG. 9 shows the results of simulation calculations. It may beseen from FIG. 9 that the conversion efficiency Eff of a solar cellmodel, having the structure of p⁺a-Si:H/a-Si:H/n⁺a-Si:H, is 7.8%, whilethat of a solar cell model, having the structure ofp⁺μc-Si:H/a-Si:H/n⁺μc-Si:H, is 13.2%. It may thus be seen that theconversion efficiency of the solar cell model, in which the p-type andn-type semiconductor layers are micro-crystallized, is higher by afactor of approximately 1.7 than that of the solar cell model, in whichthe p-type and n-type semiconductor layers and the i-layer aremicro-crystallized.

[0091] On the other hand, the conversion efficiency Eff of a solar cellmodel, in which the p-type semiconductor layer is formed of SiC and inwhich the p-type and n-type semiconductor layers are micro-crystallized,is 14.4%, which is higher by a factor of approximately 1.8 than that ofthe solar cell model, in which the p-type and n-type semiconductorlayers and the i-layer are micro-crystallized.

[0092] It should be noted that Nakamura et al., proved the above for thesolar cell having the above-described hetero junction type structure bythe same calculation method, and that the conversion efficiency can befurther improved by combining the hetero type solar cell with the dopinglayer of the present invention.

[0093] The crystalline properties and the manner of crystallization ofthe doping layer 7 of the solar cell 10 as well as characteristics ofthe solar cell 10 can readily be confirmed in detail from FIG. 10showing the relation between the rate of crystallization and the surfacereflectance as found by the measurement of UV reflectance measurementemploying the light of 200 nm and from FIG. 11 showing the measuredresults of FTIR positive reflection.

[0094] The results of UV reflectance shown in FIG. 10 are hereinafterexplained.

[0095] The decreasing reflectance on the film surface by UV reflectionindicates the increasing light scattering on the film surface. Thus, theamount of light transmitted is decreased acutely by light scatteringbrought about by providing the doping layer 7 with an electrode layer 8such as a transparent electrically conductive film. The amount of lighttransmitted through the surface layer directly represents the amount oflight irradiated on the i-layer in the solar cell 10, so that, if thereflectance on the doping layer 7 is decreased, the amount of lightirradiated on the i-layer is decreased, thus affecting the conversionefficiency.

[0096] The results of measurement of FIG. 10 clarifies the following: Ifthe high energy laser light is directly irradiated on an a-Si:H, thereflectance is decreased, from which it may be inferred that the surfacefilm is subjected to ablation. On the other hand, if the laser light isirradiated on the surface of the structure of a-Si/a-Si:H, such as thatof the solar cell 10, the reflectance is improved, thus indicating thatthe crystallization on the structure surface is optimum.

[0097] The results of measurement of FTIR in FIG. 11 are hereinafterexplained.

[0098] Since the state of the Si—H bond, as measured by FTIR, isintimately related with the photoconductivity and dark conductivity ofthe i-layer (see, for example, M. Sumiya, M. Kawasaki, H. Koinuma;Proceedings of the 10th symposium on plasma proceeding, Osaka, I-2,1992), the characteristics of the solar cell 10 can be checked bymeasuring the state of Si—H linkage.

[0099]FIG. 11 shows the transition of the peak quantity in case of theSi—H bond contained in the entire film as measured by the positivereflection type FTIR method, that is, the transition of the amount ofthe Si—H bond contained in the film.

[0100] In FIG. 11, a plot at a location marked as-depo denotes the valueof the peak of the Si—H bond of an a-Si film formed on an a-Si:H film of600 nm in thickness by a sputtering device to a thickness ofapproximately 60 nm (▪) and that of an a-Si:H film (Δ) 600 nm inthickness. FIG. 11 shows the amount of displacement of a peak amount ofthe Si—H bond after laser irradiation in case these values arenormalized to unity (1).

[0101] Referring to FIG. 11, the surface of the a-Si/a-Si:H, which is astructure owned by the solar cell 10, or the doping layer 7 in the solarcell 10, is annealed with an excimer laser, the Si—H peaks, required fordemonstrating high photoelectric characteristics, are increased, thustestifying to improved film quality, without deterioration in the filmquality.

[0102] Conversely, should the excimer laser be irradiated on the a-Si:Hcontaining a large quantity of hydrogen in the doping layer, as astructure owned by a conventional solar cell, distinct from the solarcell 10, the process of destruction of the Si—H bond can be recognized,thus indicating that the film being formed is low in characteristics. Ifthe photoconductivity at this time is checked, the dark conductivity,which is the conductivity when the light is not irradiated on thephotoelectric conversion device is on the order of 1×10⁻⁷ S/cm, whilstthe photoconductivity as the conductivity when the light is irradiatedon the photoelectric conversion device is on the order of 1×10⁻⁵ S/cm,indicating that the difference between the dark conductivity andphotoconductivity is of an extremely small value corresponding to twodigits of magnitudes. If the difference the dark conductivity andphotoconductivity is large, the effect on light irradiation of the solarcell increases, so that, in this case, it may be is seen that theefficiency of the solar cell is lowered appreciably.

[0103] The bond density of Si—H of the poly-crystallized doping layer 7of the solar cell 10 is calculated by referring to FIG. 11.

[0104] If, on an upper part of the a-Si:H film, corresponding to theamorphous layer 6 of the solar cell 10, an a-Si, corresponding to thedoping layer 7 of the solar cell 10, is formed to a thickness ofapproximately 60 nm, and excess hydrogen in the a-Si:H film is adsorbedfollowing laser irradiation to the upper a-Si layer, the overallincrease of the Si—H bond may be regarded as being an increased amountof the Si—H bond in the a-Si film corresponding to the doping layer 7 ofthe solar cell 10 formed to a thickness of approximately 60 nm.

[0105] The density of the Si—H bond, calculated from the peak area ofthe Si—H peak, as measured from the Brodsky equation and FTIR, isapproximately 7.9×10²¹ (atom/cm³) in the as-depo, while being 8.2×10²¹(atom/cm³), 8.6×10²¹ (atom/cm³) and 8.4×10²¹ (atom/cm³) in case ofirradiation with the laser power of 185 mJ/cm², 250 mJ/cm² and 310mJ/cm², respectively.

[0106] Thus, the bond density of si-H in the sputtered layer portion inthe doping layer 7 of the solar cell 10 following crystallization bylaser irradiation is approximately 3.3×10²¹ (atom/cm³), approximately7.7×10²¹ (atom/cm³) and approximately 5.5×10²¹ (atom/cm³), for theirradiation 185 mJ/cm², 250 mJ/cm² and 310 mJ/cm², respectively.

[0107]FIG. 12 shows a photo by TEM of a polycrystalline(micro-crystal)/amorphous/polycrystalline structure prepared bydepositing an a-Si corresponding to the doping layer 7 of the solar cell10 by the sputtering device on the a-Si:H film of 600 nm in thicknesscorresponding to the amorphous layer 6 of the solar cell 10 and byirradiating the excimer laser. If laser light of a stronger energy ofapproximately 310 mJ/cm² is irradiated, there is prepared apolycrystalline area of approximately 30 nm on the surface, with thecrystal grain becoming smaller from the surface to the substrate side.If the irradiating energy is decreased, the size of the surface crystalsis naturally decreased.

[0108] For checking for the value of the doping efficiency of the dopinglayer 7 of the solar cell 10, a PH₃ plasma is directed to the a-Si filmsurface 40 nm in thickness, sputtered on the a-Si:H film, 600 nm inthickness, corresponding to the amorphous layer 6 of the solar cell 10to adsorb phosphorus, after which the excimer laser is irradiated toprepare the doping layer 7 as a polycrystalline layer doped withphosphorus.

[0109]FIG. 13 shows the results of structure observation by TEM onphosphorus doping. These results indicate that the average crystal sizeof the uppermost surface is approximately 30 nm, and that the crystalsize on averaging the crystal grain size of the entire film along thedepth-wise direction may be regarded as being approximately 10 nm.

[0110]FIG. 14 shows measured results of the phosphorus concentration bySIMS of the a-Si film, doped with phosphorous. The results by SIMS shownin FIG. 14 indicate that phosphorus is doped by approximately 1.5×10²¹atom/cm⁻³ into the a-Si film. The results of measurement of the positiveholes in the a-Si film, doped with phosphorus, indicate that the carrierdensity amounts to 1.5×10²¹ cm⁻³.

[0111] Since it may be presumed that substantially the totality ofphosphorus doped in the a-Si film contributes to the carriers of thea-Si film, it is seen that the doping efficiency of the a-Si film in itsentirety nearly equal to 100% has been achieved. On the other hand,comparison of the observed results of the structure by TEM shown in FIG.13 to the measured results of the phosphorus concentration by SIMS shownin FIG. 14 reveal that the doping efficiency for the film of the averagecrystal grain size of approximately 10 nm in the direction of depth,that is in the layering direction, of the a-Si film is approximately100%.

[0112] It may be seen from above that, since the solar cell 10 embodyingthe present invention includes the highly crystalline doping layer 7 andthe doping efficiency of the doping layer 7 is that high, it is possibleto improve the conversion efficiency.

[0113] Since the solar cell 10 is of the p-i-n structure, and thei-layer is the amorphous silicon-based thin film, the optical absorptioncoefficient of the i-layer is higher, such that the thickness of thei-layer necessary for photoelectric conversion can be one-hundredth ofthat in case of the crystalline silicon based solar cell.

[0114] Moreover, since the plastics substrate 1 is used as a substratein the solar cell 10, the solar cell can be molded to an optional shapeat a lower temperature, so that it is high in mass producibility andreduced in machining cost. Since the solar cell 10 uses the amorphousthin film, the manufacturing cost can be further suppressed as comparedto that of the bulk solar cell such as single crystal andpolycrystalline solar cell.

EXAMPLE

[0115] For clarifying the effect of the present invention further,explanation is made of several Examples for specified preparation of thesolar cell 10, and Comparative Examples for preparation of the solarcell 10 crystallized with a higher hydrogen concentration of the dopinglayer and for preparation of the solar cell having an amorphous dopinglayer.

[0116] The Example is a solar cell 10 having the doping layer 7 and theamorphous layer 6 of the μc-Si:H/a-Si:H structure, while the ComparativeExamples are the solar batteries 10 in which the doping layer 7 and theamorphous layer 6 are of the a-Si:H/a-Si:H structure.

[0117]FIG. 15 schematically shows the solar cell 10 prepared by atechnique explained in connection with the following Examples 1 to 13.These Examples are now explained by referring to FIG. 15.

Example 1

[0118] First, a PET substrate 11, carrying an acrylic resin layer 12hard-coated thereon, is rinsed and placed on a substrate holder of asputtering device with the acrylic resin layer 12 facing upwards. Thesputtering device 2 is evacuated by a vacuum pump to 10⁻⁶ Torr, whilethe surface temperature of the PET substrate 11 was set to 120° C.

[0119] On the upper surface of the acrylic resin layer 12 was formedSiO₂ to a thickness of 300 nm by reactive sputtering to form an SiO₂layer 13, which later becomes a thermal buffer layer in the course ofthe subsequent heat treatment process. Then, Al is formed by DCsputtering to a thickness of 200 nm to form an Al layer 14. An ITO layer15 then is formed to a thickness of 50 nm to form an electrode. This Allayer 14 and the ITO layer 15 are formed to serve as the electrode andas the reflecting film on the reverse surface, respectively.

[0120] Then, at a power of 1000 W, a plasma was produced and a targetsubstrate doped with phosphorus was DC sputtered to form an a-Si film of5 nm doped with phosphorus.

[0121] The film formed was irradiated with the XeCl excimer laser to amaximum of 200 mJ/cm² to form a crystallized poly-Si layer 16.

[0122] The line beam, used at this time, has an energy gradient suchthat the energy intensity is gradually increased from one end of theshort beam axis direction. By gradually scanning the film from the lowenergy strength side, the film is crystallized, as the film damage dueto emission of Ar slightly captured into the film is suppressed. Thispoly-Si layer 16 becomes a lower impurity addition layer in the solarcell 10. Here, the a-Si film, doped with phosphorus, operates as then-type semiconductor layer.

[0123] Then, on the poly-Si layer 16 was caused to flow 50 sccm of SiH₄(10%)/H₂ and, as the pressure in discharging was set to 20 mTorr and asthe surface temperature of the PET substrate 11 was set to 120° C., anon-doped a-Si—H layer 17 was formed to 600 nm. This a-Si—H layer 17becomes an optically active layer of the solar cell 10.

[0124] On this a-Si—H layer 17 were caused to flow 50 sccm of SiH₄(10%)/H₂ and 50 sccm of B₂H₆ (1%)/H₂ and, as the sputtering device wasset to the pressure in discharging of 200 mTorr and the surfacetemperature of the PET substrate 11 was 120° C., a plasma was generatedat a power of 200W, to form an a-Si:H film of 5 nm doped with boron.

[0125] Then, 30 sccm of Ar was caused to flow and the sputtering devicewas set so that the pressure in discharging was 3 mTorr and the surfacetemperature of the PET substrate 11 was 120° C. A plasma was generatedat the power of 1000W and the target substrate doped with boron was DCsputtered to form a boron-doped a-Si film of 10 nm. As in forming thepoly-Si layer 16, described above, an XeCl excimer laser was irradiatedat a maximum of 250 mJ/cm² at the maximum, in terms of a line beam, toform a μc-Si:H layer 18. This μc-Si:H layer 18 becomes an upper impurityaddition layer in the solar cell 10. Since here the layer is doped withboron, it operates as a p-type semiconductor.

[0126] An ITO target then is formed to 150 nm by RF sputtering to forman ITO layer 19. Finally, Al is formed by sputtering to 200 nm to forman Al current collector electrode 20 by lift off using a resist.

[0127] Meanwhile, the μc-Si:H layer 18 is crystallized as the crystalgrain size is gradually comminuted form the surface towards the PETsubstrate 11.

Example 2

[0128] First, the PET substrate 11, carrying the acrylic resin layer 12hard-coated thereon, is rinsed, and put on the substrate holder of thesputtering device, with the acrylic resin layer 12 directing upwards.The sputtering device is evacuated to 10⁻⁶ Torr by a vacuum pump and isset so that the surface temperature of the PET substrate 11 will be 120°C.

[0129] On the upper surface of the acrylic resin layer 12 was formedSiO₂ to a thickness of 300 nm by reactive sputtering to form an SiO₂layer 13, which later becomes a thermal buffer layer in the course ofthe subsequent heat treatment process. Then, Al is formed by DCsputtering to a thickness of 200 nm to form an Al layer 14. An ITO layer15 then is formed to a thickness of 50 nm to form an electrode. This Allayer 14 and the ITO layer 15 are formed to serve as the electrode andas the reflecting film on the reverse surface, respectively.

[0130] Then, at a power of 1000 W, a plasma was produced and a targetsubstrate doped with phosphorus was DC sputtered to form an a-Si film of5 nm doped with phosphorus.

[0131] The film formed was irradiated with the XeCl excimer laser to amaximum of 200 mJ/cm² to form a crystallized poly-Si layer 16.

[0132] The line beam, used at this time, has an energy gradient suchthat the energy intensity is gradually increased from one end of theshort beam axis direction. By gradually scanning the film from the lowenergy strength side, the film is crystallized, as the film damage dueto emission of Ar slightly captured into the film is suppressed. Thispoly-Si layer 16 becomes a lower impurity addition layer in the solarcell 10. Here, the a-Si film, doped with phosphorus, operates as thep-type semiconductor layer.

[0133] Then, on the poly-Si layer 16 was caused to flow 50 sccm of SiH₄(10%)/H₂ and, as the pressure in discharging was set to 20 mTorr and asthe surface temperature of the PET substrate 11 was set to 120° C., anon-doped a-Si—H layer 17 was formed to 600 nm. This a-Si—H layer 17becomes an optically active layer of the solar cell 10.

[0134] On this a-Si—H layer 17 were caused to flow 50 sccm of SiH₄(10%)/H₂ and 50 sccm of PH₃ (1%)/H₂ and, as the sputtering device wasset to the pressure in discharging of 200 mTorr and the surfacetemperature of the PET substrate 11 was 120° C., a plasma was generatedat a lower of 200W, to form an a-Si:H film of 5 nm doped withphosphorus.

[0135] Then, 30 sccm of Ar was caused to flow and the sputtering devicewas set so that the pressure in discharging was 3 mTorr and the surfacetemperature of the PET substrate 11 was 120° C. A plasma was generatedat the power of 1000W and the target substrate doped with phosphorus wasDC sputtered to form a phosphorus-doped a-Si film of 10 nm. As informing the poly-Si layer 16, described above, an XeCl excimer laser wasirradiated at a maximum of 250 mJ/cm² at the maximum, in terms of a linebeam, to form a μc-Si:H layer 18. This μc-Si:H layer 18 becomes an upperimpurity addition layer in the solar cell 10. Since here the layer isdoped with phosphorus, it operates as an n-type semiconductor.

[0136] An ITO target then is formed to 150 nm by RF sputtering to forman ITO layer 19. Finally, Al is formed by sputtering to 200 nm to forman Al current collector electrode 20 by lift off using a resist.

[0137] Meanwhile, the μc-Si:H layer 18 is crystallized as the crystalgrain size is gradually comminuted from the surface of the layer towardsthe PET substrate 11.

Example 3

[0138] First, the PET substrate 11, carrying the acrylic resin layer 12hard-coated thereon, is rinsed, and put on the substrate holder of thesputtering device, with the acrylic resin layer 12 directing upwards.The sputtering device is evacuated to 10⁻⁶ Torr by a vacuum pump and isset so that the surface temperature of the PET substrate 11 will be 120°C.

[0139] On the upper surface of the acrylic resin layer 12 was formedSiO₂ to a thickness of 300 nm by reactive sputtering to form an SiO₂layer 13, which later becomes a thermal buffer layer in the course ofthe subsequent heat treatment process. Then, Al is formed by DCsputtering to a thickness of 200 nm to form an Al layer 14. An ITO layer15 then is formed to a thickness of 50 nm to from an electrode. The Allayer 14 and an ITO layer 15 are formed to serve as the electrode and asthe reflecting film on the reverse surface, respectively.

[0140] Then, at a power of 1000 W, a plasma was produced and a targetsubstrate doped with boron was DC sputtered to form an a-Si film of 5 nmdoped with boron.

[0141] The film formed was irradiated with the XeCl excimer laser to amaximum of 300 mJ/cm² to form a crystallized poly-Si layer 16.

[0142] The line beam, used at this time, has an energy gradient suchthat the energy intensity is gradually increased from one end of theshort beam axis direction. By gradually scanning the film from the lowenergy strength side, the film is crystallized, as the film damage dueto emission of Ar slightly captured into the film is suppressed. Thispoly-Si layer 16 becomes a lower impurity addition layer in the solarcell 10. Here, a-Si film, doped with boron, operates as the p-typesemiconductor layer.

[0143] Then, on the poly-Si layer 16 was formed a non-dopeda-Si_(x)Ge_(1-x):H layer 17 (0<x≦1), to a thickness of 600 nm, at asurface temperature of 120° C. of the PET substrate 11. The flow ratioof GeH₄ (10%)/H₂ to SiH₄ (10%)/H₂ was gradually changed as from thestart of generation of the film so that the film composition will besuch that the proportion of x in the a-Si_(x)Ge_(1-x):H layer 17 will beincreased from the side PET substrate 11, with the flow of GeH₄ (10%)/H₂being interrupted as from a mid stage. This a-Si_(x)Ge_(1-x):H layer 17(0<x≦1) becomes an optically active layer of the solar cell 10.

[0144] On this a-Si_(x)Ge_(1-x):H layer 17 (0<x≦1) were caused to flow50 sccm of SiH₄ (10%)/H₂ and 50 sccm of PH₃ (1%)/H₂ and, as thesputtering device was set to the pressure in discharging of 200 mTorrand the surface temperature of the PET substrate 11 was 120° C., aplasma was generated at a power of 20W, to form an a-Si:H film of nmdoped with phosphorus.

[0145] Then, 30 seem of Ar was caused to flow and the sputtering devicewas set so that the pressure in discharging was 3 mTorr and the surfacetemperature of the PET substrate 11 was 120° C. A plasma was generatedat the power of 1000W and the target substrate doped with boron was DCsputtered to form aphosphorus-doped a-Si film of nm. As in forming thepoly-Si layer 16, described above, an XeCl excimer laser was irradiatedat a maximum of 250 mJ/cm² at the maximum, in terms of a line beam, toform a μc-Si:H layer 18. This μc-Si:H layer 18 becomes an upper impurityaddition layer in the solar cell 10. Since here the layer is dopedwithphosphorus, it operates as an n-type semiconductor.

[0146] An ITO target then is formed to 150 nm by RF sputtering to forman ITO layer 19. Finally, Al is formed by sputtering to 200 nm to forman Al current collector electrode 20 by lift off using a resist.

[0147] Meanwhile, the μc-Si:H layer 18 is crystallized as the crystalgrain size is gradually comminuted form the surface towsrdfs the PETsubstrate 11.

Example 4

[0148] First, the PET substrate 11, carrying the acrylic resin layer 12hard-coated thereon, is rinsed, and put on the substrate holder of thesputtering device, with the acrylic resin layer 12 directing upwards.The sputtering device is evacuated to 10⁻⁶ Torr by a vacuum pump and isset so that the surface temperature of the PET substrate 11 will be 120°C.

[0149] On the upper surface of the acrylic resin layer 12 was formedSiO₂ to a thickness of 300 nm by reactive sputtering to form an SiO₂layer 13, which later becomes a thermal buffer layer in the sourse ofthe subsequent heat treatment process. Then, Al is formed by DCsputtering to a thickness of 200 nm to form an Al layer 14. An ITO layer15 then is formed to a thickness of 50 nm to from an electrode. The Allayer 14 and the ITO layer 15 are formed to serve as the electrode andas the reflecting film on the reverse surface, respectively.

[0150] Then, at a power of 1000 W, a plasma was produced and a targetsubstrate doped with boron was DC sputtered to form an a-Si film of 5 nmdoped with phosphorus.

[0151] The film formed was irradiated with the XeCl excimer laser to amaximum of 200 mJ/cm² to form a crystallized poly-Si layer 16.

[0152] The line beam, used at this time, has an energy gradient suchthat the energy intensity is gradually increased from one end of thebeam short axis direction. By gradually scanning the film from the lowenergy strength side, the film is crystallized, as the film damage dueto emission of Ar slightly captured into the film is minimized. Thispoly-Si layer 16 becomes a lower impurity addition layer in the solarcell 10. Here, a-Si film, doped with phosphorus, operates as the n-typesemiconductor layer.

[0153] Then, on the poly-Si layer 16, an a-Si_(x)Ge_(1-x):H layer 17(0<x≦1) of, at a surface temperature of 120° C. of the PET substrate 11,a non-doped was formed to 600 nm. The flow ratio of GeH₄ (10%)/H₂ toSiH₄ (10%)/H₂ was gradually changed as from the start of generation ofthe film so that the film composition will be such that the proportionof x in the a-Si_(x)Ge_(1-x):H layer 17 (0<x≦1) will be increased fromthe side PET substrate 11, with the flow of GeH₄ (10%)/H₂ beinginterrupted as from a mid stage. This a-Si_(x)Ge_(1-x):H layer 17(0<x≦1) becomes an optically active layer of the solar cell 10.

[0154] On this a-Si_(x)Ge_(1-x):H layer 17 (0<x≦1) were caused to flow50 sccm of SiH₄ (10%)/H₂ and 50 sccm of B₂H₆ (1%)/H₂ and, as thesputtering device was set to the pressure in discharging of 200 mTorrand the surface temperature of the PET substrate 11 was 120° C., aplasma was generated at a lower of 20W, to form an a-Si:H film of 5 nmdoped with boron.

[0155] Then, 30 sccm of Ar was caused to flow and the sputtering devicewas set so that the pressure in discharging was 3 mTorr and the surfacetemperature of the PET substrate 11 was 120° C. A plasma was generatedat the power of 1000W and the target substrate doped with boron was DCsputtered to form a boron-doped a-Si film of 10 nm. As in forming thepoly-Si layer 16, described above, an XeCl excimer laser was irradiatedat a maximum of 250 mJ/cm², in terms of a line beam, to form a μc-Si:Hlayer 18. This μc-Si:H layer 18 becomes an upper impurity addition layerin the solar cell 10. Since here the layer is doped with boron, itoperates as a p-type semiconductor.

[0156] An ITO target then is formed to 150 nm by RF sputtering to forman ITO layer 19. Finally, Al is formed by sputtering to 200 nm to forman Al current collector electrode 20 by lift off using a resist.

[0157] Meanwhile, the μc-Si:H layer 18 is crystallized as the crystalgrain size is gradually comminuted form the surface towards the PETsubstrate 11.

Example 5

[0158] First, the PET substrate 11, carrying the acrylic resin layer 12hard-coated thereon, is rinsed, and put on the substrate holder of thesputtering device, with the acrylic resin layer 12 directing upwards.The sputtering device is evacuated to 10⁻⁶ Torr by a vacuum pump and isset so that the surface temperature of the PET substrate 11 will be 120°C.

[0159] On the upper surface of the acrylic resin layer 12 was formedSiO₂ to a thickness of 300 nm by reactive sputtering to form an SiO₂layer 13, which later becomes a thermal buffer layer in the course ofthe subsequent heat treatment process. Then, Al is formed by DCsputtering to a thickness of 200 nm to form an Al layer 14. An ITO layer15 then is formed to a thickness of 50 nm to from an electrode. The Allayer 14 and the ITO layer 15 are formed to serve as the electrode andas the reflecting film on the reverse surface, respectively.

[0160] Then, at a power of 1000 W, a plasma was produced and a targetsubstrate doped with boron was DC sputtered to form an a-Si film of 10nm doped with boron.

[0161] The film formed was irradiated with the XeCl excimer laser to amaximum of 300 mJ/cm² to form a crystallized poly-Si layer 16.

[0162] The line beam, used at this time, has an energy gradient suchthat the energy intensity is gradually increased from one end of theshort beam axis direction. By gradually scanning the film from the lowenergy strength side, the film is crystallized, as the film damage dueto emission of Ar slightly captured into the film is minimized. Thispoly-Si layer 16 becomes a lower impurity addition layer in the solarcell 10. Here, a-Si film, doped with boron, operates as the p-typesemiconductor layer.

[0163] Then, on the poly-Si layer 16 was caused to flow 50 sccm of SiH₄(10%)/H₂ and, as the pressure in discharging was set to 20 mTorr and asthe surface temperature of the PET substrate 11 was set to 120° C., anon-doped a-Si—H layer 17 was formed to 600 nm. This a-Si—H layer 17becomes an optically active layer of the solar cell 10.

[0164] Then, 30 sccm of Ar was caused to flow and the sputtering devicewas set so that the pressure in discharging was 3 mTorr and the surfacetemperature of the PET substrate 11 was 120° C. A plasma was generatedat the power of 1000W and the target substrate doped with boron was DCsputtered to form a boron-doped a-Si film of 10 nm. As in forming thepoly-Si layer 16, described above, an XeCl excimer laser was irradiatedat a maximum of 250 mJ/cm², in terms of a line beam, to form a μc-Si:Hlayer 18. This μc-Si:H layer 18 becomes an upper impurity addition layerin the solar cell 10. Since here the μc-Si:H layer is doped withphosphorus, it operates as a n-type semiconductor.

[0165] An ITO target then is formed to 150 nm by RF sputtering to forman ITO layer 19. Finally, Al is formed by sputtering to 200 nm to forman Al current collector electrode 20 by lift off using a resist.

[0166] Meanwhile, the μc-Si:H layer 18 is crystallized as the crystalgrain size is gradually comminuted from the layer surface towards thePET substrate 11.

Example 6

[0167] First, the PET substrate 11, carrying the acrylic resin layer 12,hard-coated thereon, is rinsed, and put on the substrate holder of thesputtering device, with the acrylic resin layer 12 directing upwards.The sputtering device is evacuated to 10⁻⁶ Torr by a vacuum pump and isset so that the surface temperature of the PET substrate 11 will be 120°C.

[0168] On the upper surface of the acrylic resin layer 12 was formedSiO₂ to a thickness of 300 nm by reactive sputtering to form an SiO₂layer 13, which later becomes a thermal buffer layer in the course ofthe subsequent heat treatment process. Then, Al is formed by DCsputtering to a thickness of 200 nm to form an Al layer 14. An ITO layer15 then is formed to a thickness of 50 nm to from an electrode. This Allayer 14 and the ITO layer 15 are formed to serve as the electrode andas the reflecting film on the reverse surface, respectively.

[0169] Then, at a power of 1000 W, a plasma was produced and a targetsubstrate doped with phosphorus was DC sputtered to form an a-Si film of10 nm doped with phosphorus.

[0170] The film formed was irradiated with the XeCl excimer laser to amaximum of 300 mJ/cm² to form a crystallized poly-Si layer 16.

[0171] The line beam, used at this time, has an energy gradient suchthat the energy intensity is gradually increased from one end of theshort beam axis direction. By gradually scanning the film from the lowenergy strength side, the film is crystallized, as the film damage dueto emission of Ar slightly captured into the film is minimized. Thispoly-Si layer 16 becomes a lower impurity addition layer in the solarcell 10. Here, the a-Si film, doped with phosphorus, operates as then-type semiconductor layer.

[0172] Then, on the poly-Si layer 16 was caused to flow 50 sccm of SiH₄(10%)/H₂ and, as the pressure in discharging was set to 20 mTorr and asthe surface temperature of the PET substrate 11 was set to 120° C., anon-doped a-Si—H layer 17 was formed to 600 nm. This a-Si—H layer 17becomes an optically active layer of the solar cell 10.

[0173] Then, 30 sccm of Ar was caused to flow and the sputtering devicewas set so that the pressure in discharging was 3 mTorr and the surfacetemperature of the PET substrate 11 was 120° C. A plasma was generatedat the power of 1000W and the target substrate doped with boron was DCsputtered to form a boron-doped a-Si film of 10 nm. As in forming thepoly-Si layer 16, described above, an XeCl excimer laser was irradiatedat a maximum of 250 mJ/cm², in terms of a line beam, to form a μc-Si:Hlayer 18. This μc-Si:H layer 18 becomes an upper impurity addition layerin the solar cell 10. Since here the layer is doped with boron, itoperates as a p-type semiconductor.

[0174] An ITO target then is formed to 150 nm by RF sputtering to forman ITO layer 19. Finally, Al is formed by sputtering to 200 nm to forman Al current collector electrode 20 by lift off using a resist.

[0175] Meanwhile, the μc-Si:H layer 18 is crystallized as the crystalgrain size is gradually comminuted form the surface towards the PETsubstrate 11.

Example 7

[0176] First, the PET substrate 11, carrying the acrylic resin layer 12,hard-coated thereon, is rinsed, and put on the substrate holder of thesputtering device, with the acrylic resin layer 12 directing upwards.The sputtering device is evacuated to 10⁻⁶ Torr by a vacuum pump and isset so that the surface temperature of the PET substrate 11 will be 120°C.

[0177] On the upper surface of the acrylic resin layer 12 was formedSiO₂ to a thickness of 300 nm by reactive sputtering to form an SiO₂layer 13, which later becomes a thermal buffer layer in the course ofthe subsequent heat treatment process. Then, Ag is formed by DCsputtering to a thickness of 200 nm to form an Ag layer 14. A ZnO; Allayer 15 then is formed to a thickness of 50 nm by reactive sputteringto form an electrode. This Ag layer 14 and the ZnO; Al layer 15 areformed to serve as the electrode and as the reflecting film on thereverse surface, respectively.

[0178] The electrode was placed on the substrate holder of thesputtering device, with the surface thereof carrying this ZnO; Al layer15 directing upwards, and evacuated to approximately 10⁻⁶ Torr, using avacuum pump. A plasma was formed at a power of 1000 W and the targetsubstrate doped with phosphorus was DC sputtered to form an a-Sisubstrate of 10 nm doped with phosphorus.

[0179] The film formed was irradiated with the XeCl excimer laser to amaximum of 300 mJ/cm² to form a crystallized poly-Si layer 16.

[0180] The line beam, used at this time, has an energy gradient suchthat the energy intensity is gradually increased from one end of thebeam short axis direction. By gradually scanning the film from the lowenergy strength side, the film is crystallized, as the film damage dueto emission of Ar slightly captured into the film is minimized. Thispoly-Si layer 16 becomes a lower impurity addition layer in the solarcell 10. Here, a-Si film, doped with phosphorus, operates as the n-typesemiconductor layer.

[0181] Then, on the poly-Si layer 16 was caused to flow 50 sccm of SiH₄(10%)/H₂ and, as the pressure in discharging was set to 20 mTorr and asthe surface temperature of the PET substrate 11 was set to 120° C., anon-doped a-Si—H layer 17 was formed to 600 nm. This a-Si—H layer 17becomes an optically active layer of the solar cell 10.

[0182] On an upper surface of the non-doped a-Si:H layer 17 was formedan a-Si film, to 30 nm, using a target, doped with boron, by asputtering method.

[0183] On this a-Si film, 50 sccm of H₂ and 10 sccm of B₂H₆ (1%)/H₂ werecaused to flow for exposure to a plasma generated at 20W for threeminutes. An XeCl excimer laser was irradiated in a line beam of 250mJ/cm² at the maximum to carry out crystallization and dopingsimultaneously to form a μc-Si:H layer 18, which layer 18 later becomesan upper impurity addition layer in the solar cell 10. Here, the a-Silayer, doped with boron, operates as a p-type semiconductor.

[0184] Then, an ITO target film is formed to 150 nm by RF sputtering toform an ITO layer 19. Finally, Al is formed to 200 nm by sputtering andan Al current collecting electrode 20 was formed by lift-off employing aresist.

[0185] Meanwhile, the μc-Si:H layer 18 is crystallized as the crystalgrain size is progressively reduced from the surface towards the PETsubstrate 11.

Example 8

[0186] First, the PET substrate 11, carrying the acrylic resin layer 12,hard-coated thereon, is rinsed and placed on the substrate holder of thesputtering device, with the acrylic resin layer 12 facing upwards. Thesputtering device was evacuated by a vacuum pump to 10⁻⁶ Torr and thesurface tem of the PET substrate 11 was set to 120° C.

[0187] On the upper surface of the acrylic resin layer 12, an SiO₂ film13 was formed to 300 nm by reactive sputtering to form an SiO₂ layer 13,which later becomes a thermal buffer layer in the course of thesubsequent heat treatment process. Then, Ag is formed by DC sputteringto a thickness of 200 nm to form an Ag layer 14. A ZnO; Al layer 15 thenis formed to a thickness of 50 nm to form an electrode. This Ag layer 14and the ZnO; Al layer 15 are formed to serve as the electrode and as thereflecting film on the reverse surface, respectively.

[0188] The electrode was placed on the substrate holder of thesputtering device, with the surface thereof carrying this ZnO; Al layer15 directing upwards, and evacuated to approximately 10⁻⁶ Torr, using avacuum pump. A plasma was formed at a power of 1000 W and th targetsubstrate doped with boron was DC sputtered to form an a-Si substrate of10 nm doped with boron.

[0189] The film formed was irradiated with the XeCl excimer laser to amaximum of 300 mJ/cm² to form a crystallized poly-Si layer 16.

[0190] The line beam, used at this time, has an energy gradient suchthat the energy intensity is gradually increased from one end of theshort beam axis direction. By gradually scanning the film from the lowenergy strength side, the film is crystallized, as the film damage dueto emission of Ar slightly captured into the film is minimized. Thispoly-Si layer 16 becomes a lower impurity addition layer in the solarcell 10. Here, the a-Si film, doped with boron, operates as the p-typesemiconductor layer.

[0191] Then, on the poly-Si layer 16 was caused to flow 50 sccm of SiH₄(10%)/H₂ and, as the pressure in discharging was set to 20 mTorr and asthe surface temperature of the PET substrate 11 was set to 120° C., anon-doped a-Si—H layer 17 was formed to 600 nm. This a-Si—H layer 17becomes an optically active layer of the solar cell 10.

[0192] On an upper surface of the non-doped a-Si:H layer 17 was formedan a-Si film, to 30 nm, using a target, doped with phosphorus, by asputtering method.

[0193] On this a-Si film, 50 sccm of H₂ and 10 sccm of PH₃ (1%)/H₂ werecaused to flow for exposure for three minutes to a plasma generated at20W. An XeCl excimer laser was irradiated in a line beam of 250 mJ/cm²at the maximum to carry out crystallization and doping simultaneously toform a μc-Si:H layer 18, which layer 18 later becomes an upper impurityaddition layer in the solar cell 10. Here, the a-Si layer, doped withphosphorus, operates as an n-type semiconductor.

[0194] Then, an ITO target film is formed to 150 nm by RF sputtering toform an ITO layer 19. Finally, AL is formed to 200 nm by sputtering andan Al current collecting electrode 20 was formed by lift-off employing aresist.

[0195] Meanwhile, the μc-Si:H layer 18 is crystallized as the crystalgrain size is progressively reduced from the surface towards the PETsubstrate 11.

Example 9

[0196] First, the PET substrate 11, carrying the acrylic resin layer 12,hard-coated thereon, is rinsed and placed on the substrate holder of thesputtering device, with the acrylic resin layer 12 facing upwards. Thesputtering device was evacuated by a vacuum pump to 10⁻⁶ Torr and thesurface temperature of the PET substrate 11 was set to 120° C.

[0197] On the upper surface of the acrylic resin layer 12, an SiO₂ filmwas formed to 300 nm by reactive sputtering to form an SiO₂ layer 13,which later becomes a thermal buffer layer in the course of thesubsequent heat treatment process. Then, Ag is formed by DC sputteringto a thickness of 200 nm to form an Ag layer 14. A ZnO; Al layer 15 thenis formed to a thickness of 50 nm to from an electrode. This Ag layer 14and the ZnO; Al layer 15 are formed to serve as the electrode and as thereflecting film on the reverse surface, respectively.

[0198] The electrode was placed on the substrate holder of thesputtering device, with the surface thereof carrying this ZnO; Al layer15 directing upwards, and was evacuated to approximately 10⁻⁶ Torr,using a vacuum pump. A plasma was formed at a power of 1000 W and thtarget substrate doped with phosphorus was DC sputtered to form an a-Sisubstrate of 10 nm doped with phosphorus.

[0199] On this a-Si film, 50 sccm of H₂ and 10 sccm of PH₃ (1%)/H₂ werecaused to flow for exposure to a plasma generated at 20W. The filmformed was irradiated with the XeCl excimer laser to a maximum of 300mJ/cm² to form a crystallized poly-Si layer 16.

[0200] The line beam, used at this time, has an energy gradient suchthat the energy intensity is gradually increased from one end of theshort beam axis direction. By gradually scanning the film from the lowenergy strength side, the film is crystallized, as the film damage dueto emission of Ar slightly captured into the film is minimized. Thispoly-Si layer 16 becomes a lower impurity addition layer in the solarcell 10. Here, the a-Si film, doped with phosphorus, operates as then-type semiconductor layer.

[0201] Then, on the poly-Si layer 16, 50 sccm of SiH₄ (10%)/H₂ wascaused to flow and, as the pressure in discharging was set to 20 mTorrand as the surface temperature of the PET substrate 11 was set to 120°C., a non-doped a-Si—H layer 17 was formed to 600 nm. This a-Si—H layer17 becomes an optically active layer of the solar cell 10.

[0202] On an upper surface of the non-doped a-Si:H layer 17 was formedan a-Si film, to 30 nm, using a target, doped with boron, by asputtering method.

[0203] On this a-Si film, 50 sccm of H₂ and 10 sccm of B₂H₆ (1%)/H₂ werecaused to flow for exposure to a plasma generated at 20W. An XeClexcimer laser was irradiated in a line beam of 250 mJ/cm² at the maximumto carry out crystallization and doping simultaneously to form a μc-Si:Hlayer 18, which layer 18 later becomes an upper impurity addition layerin the solar cell 10. Here, the a-Si layer, doped with boron, operatesas a p-type semiconductor.

[0204] Then, an ITO target film is formed to 150 nm by RF sputtering toform an ITO layer 19. Finally, AL is formed to 200 nm by sputtering andan Al current collecting electrode 20 was formed by lift-off employing aresist.

[0205] Meanwhile, the μc-Si:H layer 18 is crystallized as the crystalgrain size is progressively reduced from the surface towards the PETsubstrate 11.

Example 10

[0206] First, the PET substrate 11, carrying the acrylic resin layer 12,hard-coated thereon, is rinsed and placed on the substrate holder of thesputtering device, with the acrylic resin layer 12 facing upwards. Thesputtering device was evacuated by a vacuum pump to 10⁻⁶ Torr and thesurface tern of the PET substrate 11 was set to 120° C.

[0207] On the upper surface of the acrylic resin layer 12, an SiO₂ filmwas formed to 300 nm by reactive sputtering to form an SiO₂ layer 13,which later becomes a thermal buffer layer in the course of thesubsequent heat treatment process. Then, Ag is formed by DC sputteringto a thickness of 200 nm to form an Ag layer 14. A ZnO; Al layer 15 thenis formed to a thickness of 50 nm to from an electrode. This Ag layer 14and the ZnO; Al layer 15 are formed to serve as the electrode and as thereflecting film on the reverse surface, respectively.

[0208] The electrode was placed on the substrate holder of thesputtering device, with the surface thereof carrying this ZnO; Al layer15 directing upwards, and evacuated to approximately 10⁻⁶ Torr, using avacuum pump. A plasma was formed at a power of 1000 W and th targetsubstrate doped with phosphorus was DC sputtered to form an a-Sisubstrate of 10 nm doped with phosphorus.

[0209] On this a-Si film, 50 sccm of H₂ and 10 sccm of PH₃ (1%)/H₂ werecaused to flow for exposure for three minutes to a plasma generated at20W. The film formed was irradiated with the XeCl excimer laser to amaximum of 3000 mJ/cm² to effect crystallization and dopingsimultaneously to form a crystallized poly-Si layer 16.

[0210] The line beam, used at this time, has an energy gradient suchthat the energy intensity is gradually increased from one end of thebeam short axis direction. By gradually scanning the film from the lowenergy strength side, the film is crystallized, as the film damage dueto emission of Ar slightly captured into the film. This poly-Si layer 16becomes a lower impurity addition layer in the solar cell 10. Here, thepoly-Si film, doped with phosphorus, operates as the n-typesemiconductor layer.

[0211] Then, on the poly-Si layer 16, a non-doped a-Si_(x)Ge_(1-x):H(0<x≦1) layer 17 was formed to 600 nm, at a surface temperature of thePET substrate 11 of 120° C. The flow ratio of GeH₄ (10%)/H₂ to SiH₄(10%)/H₂ was gradually changed as from the start of generation of thefilm so that the film composition will be such that the proportion of xin the a-Si_(x)Ge_(1-x):H layer 17 (0<x≦1) will be increased from theside PET substrate 11, with the flow of GeH₄ (10%)/H₂ being interruptedas from a mid stage, to form the a-Si:H (x=1) film. Thisa-Si_(x)Ge_(1-x):H layer 17 (0<x≦1) becomes an optically active layer ofthe solar cell 10.

[0212] On an upper surface of the non-doped a-Si_(x)Ge_(1-x):H layer 17(0<x≦1) was formed an a-Si film, to 30 nm, using a target, doped withboron, by a sputtering method.

[0213] On this a-Si film, 50 sccm of H₂ and 10 sccm of B₂H₆ (1%)/H₂ werecaused to flow for exposure to a plasma generated at 20W for threeminutes. An XeCl excimer laser was irradiated in a line beam of 250mJ/cm² at the maximum to carry out crystallization and dopingsimultaneously to form a μc-Si:H layer 18, which layer 18 later becomesan upper impurity addition layer in the solar cell 10. Here, the μc-Si:Hlayer 18, doped with boron, operates as a p-type semiconductor.

[0214] Then, an ITO target film is formed to 150 nm by RF sputtering toform an ITO layer 19. Finally, Al is formed to 200 nm by sputtering andan Al current collecting electrode 20 was formed by lift-off employing aresist.

[0215] Meanwhile, the μc-Si:H layer 18 is crystallized as the crystalgrain size is progressively reduced from the surface towards the PETsubstrate 11.

Example 11

[0216] First, the PET substrate 11, carrying the acrylic resin layer 12,hard-coated thereon, is rinsed and placed on the substrate holder of thesputtering device, with the acrylic resin layer 12 facing upwards. Thesputtering device was evacuated by a vacuum pump to 10⁻⁶ Torr and thesurface tem of the PET substrate 11 was set to 120° C.

[0217] On the upper surface of the acrylic resin layer 12, an SiO₂ filmwas formed to 300 nm by reactive sputtering to form an SiO₂ layer 13,which later becomes a thermal buffer layer in the course of thesubsequent heat treatment process. Then, Ag is formed by DC sputteringto a thickness of 200 nm to form an Ag layer 14. A ZnO; Al layer 15 thenis formed to a thickness of 50 nm to from an electrode. This Ag layer 14and the ZnO; Al layer 15 are formed to serve as the electrode and as thereflecting film on the reverse surface, respectively.

[0218] The electrode was placed on the substrate holder of thesputtering device, with the surface thereof carrying this ZnO; Al layer15 directing upwards, and evacuated to approximately 10⁻⁶ Torr, using avacuum pump. A plasma was formed at a power of 1000 W and the targetsubstrate doped with phosphorus was DC sputtered to form an a-Sisubstrate of 10 nm doped with phosphorus.

[0219] On this a-Si film, 50 sccm of H₂ and 10 sccm of PH₃ (1%)/H₂ werecaused to flow for exposure for three minutes to a plasma generated at20W. The film formed was irradiated with the XeCl excimer laser to amaximum of 3000 mJ/cm² to effect crystallization and dopingsimultaneously to form a crystallized poly-Si layer 16.

[0220] The line beam, used at this time, has an energy gradient suchthat the energy intensity is gradually increased from one end of theshort beam axis direction. By gradually scanning the film from the lowenergy strength side, the film is crystallized, as the film damage dueto emission of Ar slightly captured into the film is minimized. Thispoly-Si layer 16 becomes a lower impurity addition layer in the solarcell 10. Here, the poly-Si layer, doped with phosphorus, operates as then-type semiconductor layer.

[0221] Then, on the poly-Si layer 16, a non-doped a-Si_(x)Ge_(1-x):H(0<x≦1) layer 17 was formed to 600 nm, at a surface temperature of thePET substrate 11 of 120° C. The flow ratio of GeH₄ (10%)/H₂ to SiH₄(10%)/H₂ was gradually changed as from the start of generation of thefilm so that the film composition will be such that the proportion of xin the a-Si_(x)Ge_(1-x):H (0<x≦1) layer 17 will be increased from theside PET substrate 11, with the flow of GeH₄ (10%)/H₂ being interruptedas from a mid stage, to form the a-Si:H (x=1) film. Thisa-Si_(x)Ge_(1-x):H (0<x≦1) layer 17 becomes an optically active layer ofthe solar cell 10.

[0222] On an upper surface of the non-doped a-Si_(x)Ge_(1-x):H (0<x≦1)layer 17 was formed an a-Si_(x)C_(1-x) film, to 30 nm, using anSi_(x)C_(1-x) target, doped with boron, by a sputtering method.

[0223] On this a-Si_(x)C_(1-x) film, 50 sccm of H₂ and 10 sccm of B₂H₆(1%)/H₂ were caused to flow for exposure to a plasma generated at 20Wfor three minutes. An XeCl excimer laser was irradiated in a line beamof 250 mJ/cm² at the maximum to carry out crystallization and dopingsimultaneously to form a μc-Si:H layer 18, which layer 18 later becomesan upper impurity addition layer in the solar cell 10. Here, the μc-Si:Hlayer 18, doped with boron, operates as a p-type semiconductor.

[0224] Then, an ITO target film is formed to 150 nm by RF sputtering toform an ITO layer 19. Finally, Al is formed to 200 nm by sputtering andan Al current collecting electrode 20 was formed by lift-off employing aresist.

[0225] Meanwhile, the μc-Si:H layer 18 is crystallized as the crystalgrain size is progressively reduced from the layer surface towards thePET substrate 11.

Example 12

[0226] First, the PET substrate 11, carrying the acrylic resin layer 12,hard-coated thereon, is rinsed and placed on the substrate holder of thesputtering device, with the acrylic resin layer 12 facing upwards. Thesputtering device was evacuated by a vacuum pump to 10⁻⁶ Torr and thesurface tem of the PET substrate 11 was set to 120° C.

[0227] On the upper surface of the acrylic resin layer 12, an SiO₂ filmwas formed to 300 nm by reactive sputtering to form an SiO₂ layer 13,which later becomes a thermal buffer layer in the course of thesubsequent heat treatment process.

[0228] Then, using a Zn; Al target, a ZnO; Al layer 15 then is formed toa thickness of 50 nm to form an electrode. This ZnO; Al layer 15 isformed to serve as the electrode and as the reflecting film on thereverse surface.

[0229] The electrode was placed on the substrate holder of thesputtering device, with the surface thereof carrying this ZnO; Al layer15 directing upwards, and evacuated to approximately 10⁻⁶ Torr, using avacuum pump. A plasma was formed at a power of 1000 W and the targetsubstrate doped with boron was DC sputtered to form an a-Si_(x)C_(1-x)film of 10 nm doped with boron.

[0230] On this a-Si_(x)C_(1-x):H film, 50 sccm of H₂ and 10 sccm of B₂H₆(1%)/H₂ were caused to flow for exposure to a plasma generated at 20Wfor three minutes. An XeCl excimer laser was irradiated in a line beamof 300 mJ/cm² at the maximum to carry out crystallization and dopingsimultaneously to form a poly-Si layer 16.

[0231] The line beam, used at this time, has an energy gradient suchthat the energy intensity is gradually increased from one end of theshort beam axis direction. By gradually scanning the film from the lowenergy strength side, the film is crystallized, as the film damage dueto emission of Ar slightly captured into the film is minimized. Thispoly-Si layer 16 becomes a lower impurity addition layer in the solarcell 10. Here, the poly-Si film, doped with boron, operates as thep-type semiconductor layer.

[0232] Then, on the poly-Si layer 16, a non-doped a-Si_(x)Ge_(1-x):H(0<x≦1) layer 17 was formed to 600 nm, at a surface temperature of thePET substrate 11 of 120° C. The flow ratio of GeH₄ (10%)/H₂ to SiH₄(10%)/H₂ was gradually changed as from the start of generation of thefilm so that the film composition will be such that the proportion of xin the a-Si_(x)Ge_(1-x):H (0<x≦1) layer 17 will be decreased from theside PET substrate 11. This a-Si_(x)Ge_(1-x):H (0<x≦1) layer 17 becomesan optically active layer of the solar cell 10.

[0233] On an upper surface of the non-doped a-Si:H layer 17 was formedan a-Si film, to 30 nm, using a target, doped with phosphorus, by asputtering method.

[0234] On this a-Si film, 50 sccm of H₂ and 10 sccm of PH₃ (1%)/H₂ werecaused to flow for exposure to a plasma generated at 20W. An XeClexcimer laser was irradiated in a line beam of 250 mJ/cm² at the maximumto carry out crystallization and doping simultaneously to form a μc-Si:Hlayer 18, which layer 18 later becomes an upper impurity addition layerin the solar cell 10. Here, the μc-Si:H layer, doped with phosphorus,operates as a n-type semiconductor.

[0235] Finally, Al is formed to 200 nm by sputtering and an Al currentcollecting electrode 20 was formed by lift-off employing a resist. ThisAl current collecting electrode 20 operates as a reverse surfaceelectrode and as the reverse surface reflecting surface simultaneously.

[0236] Meanwhile, the μc-Si:H layer 18 is crystallized as the crystalgrain size is progressively reduced from the surface towards the PETsubstrate 11.

Example 13

[0237] First, the PET substrate 11, carrying the acrylic resin layer 12,hard-coated thereon, is rinsed and placed on the substrate holder of thesputtering device, with the acrylic resin layer 12 facing upwards. Thesputtering device was evacuated by a vacuum pump to 10⁻⁶ Torr and thesurface tem of the PET substrate 11 was set to 120° C.

[0238] On the upper surface of the acrylic resin layer 12, an SiO₂ filmwas formed to 300 nm by reactive sputtering to form an SiO₂ layer 13,which later becomes a thermal buffer layer in the course of thesubsequent heat treatment process. Then, Ag is formed by DC sputteringto a thickness of 200 nm to form an Ag layer 14. A ZnO; Al layer 15 thenis formed to a thickness of 50 nm by reactive sputtering to form anelectrode. This Ag layer 14 and the ZnO; Al layer 15 are formed to serveas the electrode and as the reflecting film on the reverse surface,respectively.

[0239] The electrode was placed on the substrate holder of thesputtering device, with the surface thereof carrying this ZnO; Al layer15 directing upwards, and was evacuated to approximately 10⁻⁷ Torr,using a vacuum pump. Then, 50 sccm of SiH₄(10%)/H₂ and 10 sccm ofPH₃(1%)/H₂ were caused to flow to generate a plasma at 20W to form ana-Si substrate of 10 nm doped with phosphorus.

[0240] The substrate, now carrying the a-Si film, was transported invacuum to a sputtering chamber and an a-Si_(x)Ge_(1-x) target substratewas DC-sputtered to form an a-Si_(x)Ge_(1-x) film 30 nm in thickness.The film formed was irradiated with the XeCl excimer laser to a maximumof 250 mJ/cm² to form a crystallized poly-Si layer 16.

[0241] The line beam, used at this time, has an energy gradient suchthat the energy intensity is gradually increased from one end of thebeam short axis direction. By gradually scanning the film from the lowenergy strength side, the film is crystallized, as the film damage dueto emission of Ar slightly captured into the film. This poly-Si layer 16becomes a lower impurity addition layer in the solar cell 10. Here, a-Sifilm, doped with phosphorus, operates as the n-type semiconductor layer.

[0242] Then, on the poly-Si layer 16, a non-doped a-Si_(x)Ge_(1-x):H(0<x≦1) layer 17 was formed to 600 nm, at a surface temperature of thePET substrate 11 of 120° C. The flow ratio of GeH₄ (10%)/H₂ to SiH₄(10%)/H₂ was gradually changed as from the start of generation of thefilm so that the film composition will be such that the proportion of xin the a-Si_(x)Ge_(1-x):H (0<x≦1) layer 17 will be increased from theside PET substrate 11, with the flow of GeH₄ (10%)/H₂ being interruptedas from a mid stage. This a-Si_(x)Ge_(1-x):H layer 17 (0<x≦1) becomes anoptically active layer of the solar cell 10.

[0243] On an upper surface of the non-doped a-Si_(x)Ge_(1-x):H (0<x≦1)layer 17 was formed an a-Si_(x)C_(1-x) film, to 30 nm, using aSi_(x)C_(1-x) target, doped with boron, by a sputtering method.

[0244] On this a-Si_(x)C_(1-x) film, 50 sccm of H₂ and 10 sccm of B₂H₆(1%) were caused to flow for exposure to a plasma generated at 20W forthree minutes. An XeCl excimer laser was irradiated in a line beam of250 mJ/cm² at the maximum to carry out crystallization and dopingsimultaneously to form a μc-Si:H layer 18, which layer 18 later becomesan upper impurity addition layer in the solar cell 10. Here, the μc-Si:Hlayer 18, doped with boron, operates as a p-type semiconductor.

[0245] Then, an ITO target film is formed to 150 nm by RF sputtering toform an ITO layer 19. Finally, Al is formed to 200 nm by sputtering andan Al current collecting electrode 20 was formed by lift-off employing aresist.

[0246] Meanwhile, the μc-Si:H layer 18 is crystallized as the crystalgrain size is progressively reduced from the surface towards the PETsubstrate 11.

[0247]FIG. 16 schematically shows a solar cell 30, prepared by atechnique shown in the following Comparative Example 1.

Comparative Example 1

[0248] First, a PET substrate 31, carrying an acrylic resin layer 32,hard-coated thereon, is rinsed and placed on the substrate holder of thesputtering device, with the acrylic resin layer 32 facing upwards. Thesputtering device was evacuated by a vacuum pump to 10⁻⁶ Torr and thesurface temperature of the PET substrate 11 was set to 120° C.

[0249] On the upper surface of the acrylic resin layer 32, an SiO₂ filmwas formed to 300 nm by reactive sputtering to form an SiO₂ layer 33,which later becomes a thermal buffer layer in the course of thesubsequent heat treatment process. Then, Al is formed by DC sputteringto a thickness of 200 nm to form an Al layer 34. A ITO layer 35 then isformed to a thickness of 50 nm to form an electrode. This Al layer 34and the ITO layer 35 are formed to serve as the electrode and as thereflecting film on the reverse surface, respectively.

[0250] A plasma was generated at a power of 1000 W for DC sputtering thetarget substrate doped with phosphorus to form an a-Si film of 5 nmdoped with boron.

[0251] The film formed was irradiated with the XeCl excimer laser to amaximum of 300 mJ/cm² to form a crystallized poly-Si layer 36.

[0252] The line beam, used at this time, has an energy gradient suchthat the energy intensity is gradually increased from one end of thebeam short axis direction. By gradually scanning the film from the lowenergy strength side, the film is crystallized, as the film damage dueto emission of Ar slightly captured into the film is minimized. Thispoly-Si layer 36 becomes a lower impurity addition layer in the solarcell 30. Here, the poly-Si film, doped with boron, operates as thep-type semiconductor layer.

[0253] Then, on the poly-Si layer 36 was caused to flow 50 sccm of SiH₄(10%)/H₂ and, as the pressure in discharging was set to 20 mTorr and asthe surface temperature of the PET substrate 31 was set to 120° C., anon-doped a-Si—H layer 37 was formed to 600 nm. This a-Si—H layer 37becomes an optically active layer of the solar cell 30.

[0254] On this non-doped a-Si:H layer 37, 50 sccm of SiH₄ (10%)/H₂ and50 sccm of PH₃ (1%)/H₂ were caused to flow and a sputtering device wasset so that the pressure in discharging and the surface temperature ofthe PET substrate 31 will be 200 mTorr and 120° C., respectively. Theplasma was generated at a power of 20 W to form an a-Si:H film of 15 nmdoped with phosphorus.

[0255] As in forming the poly-Si layer 36, described above, an XeClexcimer laser was irradiated in a line beam of 250 mJ/cm² at the maximumto carry out crystallization and doping simultaneously to form a μc-Si:Hlayer 38, which layer 38 later becomes an upper impurity addition layerin the solar cell 30. Here, the a-Si layer, doped with phosphorus,operates as an n-type semiconductor.

[0256] Then, an ITO target film is formed to 150 nm by RF sputtering toform an ITO layer 19. Finally, Al is formed to 200 nm by sputtering andan Al current collecting electrode 40 was formed by lift-off employing aresist.

[0257]FIG. 17 schematically shows a solar cell 50, prepared by atechnique shown in the following Comparative Example 2.

Comparative Example 2

[0258] First, a PET substrate 51, carrying an acrylic resin layer 52,hard-coated thereon, is rinsed and placed on the substrate holder of thesputtering device, with the acrylic resin layer 52 facing upwards. Thesputtering device was evacuated by a vacuum pump to 10⁻⁶ Torr and thesurface tem of the PET substrate 51 was set to 120° C.

[0259] On the upper surface of the acrylic resin layer 52, an SiO₂ filmwas formed to 300 nm by reactive sputtering to form an SiO₂ layer 53,which later becomes a thermal buffer layer in the course of thesubsequent heat treatment process. Then, Al is formed by DC sputteringto a thickness of 200 nm to form an Al layer 54. A ZnO; Al layer 55 thenis formed by reactive sputtering to a thickness of 50 nm, using a Zn; Altarget, to form an electrode. This Ag layer 54 and the ZnO; Al layer 55are formed to serve as the electrode and as the reflecting film on thereverse surface, respectively.

[0260] On this ZnO; Al layer 55, 50 sccm of SiH₄ (10%)/H₂ and 50 sccm ofPH₃ (1%)/H₂ were caused to flow and a sputtering device was set so thatthe discharging pressure and the surface temperature of the PETsubstrate 11 will be 200 mTorr and 120° C., respectively. A plasma wasgenerated at a power of 20 W to form a phosphorus-doped 15 nm a-Si:Hlayer 56.

[0261] This a-Si:H layer 56 becomes a lower impurity adding layer in thesolar cell 50. Here, the layer operated as an n-type semiconductor layerbecause it is doped with phosphorus.

[0262] On the poly-Si layer 56 was then caused to flow 50 sccm of SiH₄(10%)/H₂, as the pressure in discharging was set to 20 mTorr and asthe surface temperature of the PET substrate 51 was set to 120° C., toform a non-doped a-Si—H layer 57 to 600 nm. This a-Si—H layer 57 becomesan optically active layer of the solar cell 50.

[0263] On this non-doped a-Si—H layer 57 were then caused to flow 50sccm of SiH₄ (10%)/H₂ and 50 sccm of B₂H₆ (1%)/H₂ and, as the sputteringdevice was set so that the pressure in discharging and as the surfacetemperature of the PET substrate 11 will be 200 mTorr and 120° C.,respectively. A plasma was generated at a power of 20W to form an a-Si—Hlayer 58 of 5 nm doped with boron. This a-Si—H layer 58 becomes an upperimpurity adding layer in the solar cell 50. Since boron is here doped,the layer operates as a p-type semiconductor.

[0264] Then, an ITO target film was formed to 150 nm by RF sputtering toform an ITO layer 59. Finally, Al was formed to 200 nm by sputtering andan Al current collecting electrode 20 was formed by lift-off employing aresist.

[0265] In the Comparative Example 1, the μc-Si layer 38 of the solarcell formed appears turbid on visual inspection. The surface filmstructure is destroyed, so that the film surface scatters the light, asshown in FIG. 10. The UV reflection characteristics on the film surfaceamounted to 3%. Positive reflection characteristics by FTIR indicatedthat the Si—H bonds were destroyed appreciably. Thus, it may be inferredthat the conversion efficiency of this solar cell is approximately nil.

[0266] With the Comparative Example 2, a solar cell having the samestructure as that of the solar cell model formed solely of an amorphousstructure of p⁺a-Si:H/a-Si:H/n⁺a-Si:H was obtained. Thus, referring toFIG. 9, the conversion efficiency may be estimated to be approximately7%.

[0267] On the other hand, with the Examples 1, 4, 6, 7, 9 and 10, asolar cell 10, similar in structure to the solar cell model having thestructure of p⁺μc-Si:H/a-Si:H/n⁺μc-Si:H shown in FIG. 7 could beprepared.

[0268] Therefore, on referring to FIG. 9, the solar cell 10, prepared inthis manner, may be expected to have the conversion efficiency ofapproximately 13%. In particular, with the solar cell 10, prepared as inExamples 4 and 10, in which the i-layer could have a hetero junctionstructure, the conversion efficiency may be expected to amount to notless than 13%.

[0269] In the Examples 11 and 13, a solar cell 10 having the samestructure as that of the solar cell model having the structure ofp⁺μc-Si_(x)C_(1-x):H/a-Si:H/n⁺μc-Si:H, shown in FIG. 8, could beproduced.

[0270] So, the conversion efficiency of the solar cell 10, thusprepared, may be expected to amount to approximately 14%, as may be seenfrom FIG. 9. On the other hand, with the solar cell 10, prepared as inExamples 11 and 13, in which the i-layer could have a hetero junctionstructure, the conversion efficiency may be expected to amount to notless than 14%.

[0271] In Examples 2, 3, 5 and 8, such a solar cell 10, having astructure of n⁺μc-Si:H/a-Si:H/p⁺μc-Si:H inverted from the structure ofthe solar cell model shown in FIG. 7, could be prepared. Therefore, theconversion efficiency of the solar cell 10, thus prepared, may beexpected to be higher than that of the solar batteries of theComparative Examples 1 and 2.

[0272] In Example 12, such a solar cell 10, having a structure ofn⁺μc-Si:H/a-Si:H/p⁺μc-Si_(x)C_(1-x):H, which is an inverted structure ofthat of the solar cell model shown in FIG. 8, could be produced. On theother hand, with the solar cell 10, prepared as in Example 12, in whichthe i-layer could have a hetero junction structure, the conversionefficiency may be expected to be improved further as compared to that ofthe Examples 2, 3, 5 or 8.

[0273] The present invention may be applied not only to theabove-described solar cell but also to e.g., a photosensor.

INDUSTRIAL APPLICABILITY

[0274] In the optical energy conversion apparatus, according to thepresent invention, in which the concentration is controlled so that thehydrogen concentration in the impurity doped semiconductor layer formedon an amorphous optically active layer will be lower than that of theoptically active layer, the second impurity doped semiconductor layerforms a polycrystalline layer in which the average grain size in adirection proceeding from the surface of the semiconductor layer towardsthe substrate is decreased stepwise. Thus, by forming thepolycrystalline layer in this manner, it is possible to prevent filmdestruction by hydrogen contained in the impurity adding layer producedon crystallization by laser annealing to form the impurity adding layerinto a polycrystal having optimum crystallinity, thereby improving theconversion efficiency.

[0275] The optical energy conversion apparatus according to the presentinvention includes the impurity doped semiconductor layer which is apolycrystal having optimum crystallinity, and the amorphous opticallyactive layer, therefore an apparatus of a thin type is realized.

[0276] With the manufacturing method for the optical energy conversionapparatus according to the present invention, in which an impurity dopedsemiconductor layer having a hydrogen concentration lower than that ofthe optically active layer is formed on an amorphous optically activelayer and is subjected to laser annealing, it is possible to form apolycrystalline layer in which the average grain size of the impuritydoped semiconductor layer is decreased stepwise in the direction fromthe surface of the semiconductor layer towards the substrate.

[0277] Therefore, with the optical energy conversion apparatus, thusproduced, in which a polycrystalline impurity doped semiconductor layeris formed on the upper surface of the optically active layer, it ispossible to improve the conversion efficiency.

1. An optical energy conversion apparatus comprising: a first impuritydoped semiconductor layer, formed on a substrate, said first impuritydoped semiconductor layer being of a semiconductor material admixed witha first impurity; an optically active layer, formed on said firstimpurity doped semiconductor layer, said optically active semiconductorlayer being of a hydrogen-containing amorphous semiconductor material;and a second impurity doped semiconductor layer, admixed with a secondimpurity and formed on said optically active semiconductor layer, saidsecond impurity doped semiconductor layer being of a polycrystallizedsemiconductor material lower in hydrogen concentration than the materialof said optically active semiconductor layer; wherein the averagecrystal grain size of said second impurity doped semiconductor layer isdecreased stepwise in a direction proceeding from the surface of thesecond impurity doped semiconductor layer towards said substrate.
 2. Theoptical energy conversion apparatus according to claim 1 wherein saidfirst impurity doped semiconductor layer, said optically active layerand said second impurity doped semiconductor layer are of asilicon-based semiconductor material.
 3. The optical energy conversionapparatus according to claim 2 wherein the average hydrogenconcentration of said optically active layer is not less than 5×10²⁰atom/cc.
 4. The optical energy conversion apparatus according to claim 2wherein the average hydrogen concentration of said optically activelayer is not less than 5×10²¹ atom/cc.
 5. The optical energy conversionapparatus according to claim 2 wherein the average doping efficiency ofsaid second impurity in an area of said second impurity dopedsemiconductor layer with the average crystal grain size not less than 10nm is approximately 100%.
 6. The optical energy conversion apparatusaccording to claim 1 wherein the substrate is formed of a plasticsmaterial.
 7. The optical energy conversion apparatus according to claim1 wherein a first electrode layer is provided between said substrate andthe first impurity doped semiconductor layer and wherein a secondelectrode layer is provided on said second impurity doped semiconductorlayer.
 8. The optical energy conversion apparatus according to claim 7wherein said first and second electrode layers are formed by transparentelectrically conductive films and/or metal electrodes.
 9. The opticalenergy conversion apparatus according to claim 8 wherein saidtransparent electrically conductive films are formed of ITO, tin oxide,fluorine-doped tin oxide, zinc oxide or zinc oxide-aluminum oxide. 10.The optical energy conversion apparatus according to claim 8 whereinsaid metal electrodes are formed of Ag, Cr, Mo, Ta or Al.
 11. Theoptical energy conversion apparatus according to claim 7 wherein anadhesive layer is provided between said substrate and said firstelectrode layer.
 12. The optical energy conversion apparatus accordingto claim 1 wherein, in case light having a wavelength of 200 nm isincident on said second impurity doped semiconductor layer, thereflectance amounts to 50% or higher.
 13. The optical energy conversionapparatus according to claim 1 wherein said first impurity dopedsemiconductor layer or said second impurity doped semiconductor layer isformed of Si_(x)C_(1-x).
 14. A method for the preparation of an opticalenergy conversion apparatus comprising: forming a first impurity dopedsemiconductor layer on a substrate, said first impurity dopedsemiconductor layer being of a hydrogen-containing amorphoussemiconductor material; forming an optically active layer on said firstimpurity doped semiconductor layer, said optically active layer being ofa hydrogen-containing amorphous semiconductor material; forming a secondimpurity doped semiconductor layer on said optically active layer, saidsecond impurity doped semiconductor layer being of an amorphoussemiconductor material which is admixed with a second impurity and whichis lower in hydrogen concentration than said optically active layer; andirradiating laser light on said substrate after forming said secondimpurity doped semiconductor layer for laser annealing.
 15. The methodfor the preparation of an optical energy conversion apparatus accordingto claim 14 wherein a first electrode layer is formed on said substratebefore forming said first impurity doped semiconductor layer on saidsubstrate; and wherein a second electrode layer is formed on said secondimpurity doped semiconductor layer after forming said second impuritydoped semiconductor layer.
 16. The method for the preparation of anoptical energy conversion apparatus according to claim 14 wherein saidfirst and second impurity doped semiconductor layers are formed by asputtering device.
 17. The method for the preparation of an opticalenergy conversion apparatus according to claim 14 wherein said opticallyactive layer is formed by a sputtering device or by a CVD (chemicalvapor deposition) device.
 18. The method for the preparation of anoptical energy conversion apparatus according to claim 14 wherein saidsecond impurity doped semiconductor layer is polycrystallized as theexcimer laser is irradiated on a surface thereof.
 19. The method for thepreparation of an optical energy conversion apparatus according to claim14 wherein the power of the laser light used in laser annealing is ofsuch a level as to crystallize said second impurity doped semiconductorlayer so that the reflection index in case of incidence of light of awavelength of 200 nm on said second impurity doped semiconductor layeris not less than 50%.